I don't think there's much to do except wait and watch and provide protection from outdoor sun.
Just a bit of explanation about indoor and outdoor light here ... Indoor sun is different from outdoor sun in a couple of ways. First, it is weaker overall, fewer hours of lower intensity light. Second, it lack most of the UV present in outdoor sunlight, because regular window glass filters out most of the UV. Both of these elements combine to make it difficult for indoor plants to tolerate a lot of direct outdoor sun right away, without being given a gradual stepwise period to adjust. It is probably the UV that makes the biggest difference.
So in the future when you get the itch to give your indoor cactus some outdoor rays, give it some protection at first from the most intense, most overhead midday sun (especially during the spring and summer when that light is strongest). So maybe a position under the eaves, or next to a wall that blocks the sun for part (but not all) of the day. Dappled shade is good, filtered light is good (I have used 50-70% shade cloth). Morning sun is good, late afternoon sun is fine if it doesn't get really hot.
The exposure you give your plants is a function of intensity and time. You will get the best results by limiting both elements for the first week or two, then gradually increasing them over the course of weeks thereafter. Maybe a month into this process, your plant will be much better suited to deal with the sun, because it will have built up some resistance. But this takes weeks or months to acquire.
Most people who overwinter their cacti and other succulents indoors go through some version of this process when they bring them outside for the season. I don't have indoor plants any more but when I did, I was careful to be patient in this way when I brought them outside.
